The present invention relates generally to vehicles having multiple power sources and, more particularly, to a hybrid power system for mobile access vehicles and equipment.
Several manufacturers offer mobile access vehicles and equipment, including self-propelled and trailer-mounted boom, vertical and scissors lifts, that allow construction, maintenance and like personnel to be lifted to and suspended at high or otherwise hard-to-reach places on a job site. The advent of these access vehicles and equipment has greatly reduced the need and desire for conventional scaffolding on construction and other sites.
The great majority of mobile access vehicles manufactured and sold today are either engine-powered/hydraulically-driven, battery-powered/hydraulically-driven or battery-powered/electrically-driven. However, a small number (i.e., approximately 5% or less) of mobile access vehicles are equipped with both engines and battery packs (i.e., multi-powered) for either engine-powered or battery-powered operation, but not both at the same time.
Because the above-mentioned multi-powered access vehicles are hydraulically-driven, their efficiency is less than optimum due to power losses caused by multiple power transformations between the battery and the hydraulic drive motor(s). For example, in a conventional, battery-powered/hydraulically-driven access vehicle, the electric energy stored in the battery pack is used to power an electric motor, the electric energy is transformed into mechanical energy to power an hydraulic pump, the hydraulic pump transforms the mechanical energy into hydraulic energy to power an hydraulic drive motor, then the hydraulic energy is transformed into mechanical energy to power the wheels or other propulsion device of the vehicle.
As a result of the power transformation losses, and because the engine and the battery pack cannot be operated together to power a conventional access vehicle, the charge of the battery pack is often quickly depleted, possibly, depending on the workload, before a work shift has ended. To recharge the battery pack, the vehicle may have to be idled and connected to an external AC power source at an inconvenient time, which results in unwanted downtime and increased cost to the operator.
For an access vehicle having an on-board battery charger, the battery charger may be plugged into an external AC power source by means of an extension cord to recharge the battery pack. Even though the presence of an on-board battery charger may allow the vehicle to be operated with a depleted or low battery pack, it may be inconvenient or not recommended by the manufacturer to use the mobile vehicle while it is connected to an extension cord. As can be appreciated, a self-contained access vehicle would have a distinct advantage over one which must be plugged into an external power source to recharge its battery pack.
Furthermore, due to the power transformation losses and the anticipated peak power requirements of the vehicle, and because the battery pack and the engine cannot be operated at the same time to power the vehicle, the engine of a conventional access vehicle is sized to meet the maximum or peak power requirements of the hydraulic drive system, which occurs relatively infrequently during vehicle operation. Consequently, the engine is oversized for all other non-peak performance operations. Because fuel consumption, noise and exhaust emissions are proportionally related to engine size, it is readily apparent that an access vehicle having an engine sized for average power requirements, not the occasional peak power requirement, would be beneficial to vehicle operators and the environment.
Typically, manufacturers have sold mobile access vehicles and equipment to rental fleet operators and larger construction companies. To maximize the return on their investment, access vehicle and equipment owners must have the correct vehicle or equipment for the particular job.
Current (and anticipated) environmental laws makes it exceedingly difficult to operate engine-powered vehicles and equipment indoors. Consequently, for example, as a building construction project progresses from site preparation to an enclosed structure, engine-powered vehicles and equipment must be exchanged for or switched over to battery-powered ones.
Further, due to the increasing pace of construction projects, AC power is being installed later in the construction process than previously. If engine-powered generators are not readily available or may not be used, the lack of AC power makes it impossible to charge the battery-powered vehicles generally required for indoor use during a substantial portion of the project, resulting in the operator needing an increased number of access vehicles to complete the job.
Several automobile companies have attempted to address some of the concerns addressed above regarding battery longevity and recharging. For example, a number of automobiles which utilize a combination of battery and engine power for propulsion have been developed, such as Chrysler's Dodge Intrepid ESX and Volvo's ECC. In these automobiles, the engine is used to supplement the power output of the battery to thereby extend the driving range of the automobile, which is otherwise severely limited by the batteries. However, because automobiles are intended for only outdoor use, the "indoor" use issues discussed above regarding mobile access vehicles and equipment have not been adequately addressed by the automobile industry.
Consequently, it is apparent that rental fleet operators and access vehicle and equipment operators and owners would desire a mobile access vehicle that can operate either on battery power alone, when indoor use is required, or on a combination of engine and battery power when power demands require engine power to assist the battery or when the battery needs to be recharged.